1. Technical Field
The present disclosure relates generally to optical systems for endoscopic instrumentation and their manufacture, and, more particularly to a process for forming a relay lens system using replica molding techniques.
2. Description of Related Art
Endoscopes have long been used in surgery to view internal portions of a patient's body through a narrow incision in the body exterior or through a naturally occurring hollow viscus. Endoscopes are long, slender instruments having a shaft which is either rigid or flexible, depending upon the procedure being performed. In general, an endoscope includes an objective lens system to form an image of an object, a relay or image transmission system to transmit the image through the endoscope and an eye lens system to view the image transferred by the relay system. Examples of endoscopic optical systems are described in U.S. Pat. Nos. 3,089,484 to Hett, 3,257,902 to Hopkins, 3,556,085 to Takahachi, 4,036,218 to Yamashita, 4,267,828 to Matsuo, 4,273,110 to Groux, 4,575,195 to Hoogland, 4,545,652 to Hoogland, 4,946,267 to Hoogland, 4,964,710 to Leiner, 4,993,817 to Hoogland and 5,188,092 to White. Endoscopes are also equipped with an illumination system, such as a fiber optic bundle, which illuminates the area being imaged.
The relay lens systems of known endoscopic optical systems typically incorporate a series of field and relay lenses arranged to transfer an image through successive image planes within the system. The lens components of such conventional relay lens systems may be formed from glass, optical polymeric materials or combinations of glass lens components and polymeric components.
The decision to incorporate either glass components or polymeric components in a relay lens system for an endoscope depends upon the optical parameters to be achieved and the intended use of the endoscope, e.g., whether the scope is intended to be disposable, i.e., disposed after a single use, or wholly or partly reusable and sterilized after each use. In general, glass lens components provide enhanced optical effectiveness, but, are expensive to manufacture, requiring extensive precision grinding and polishing of the lens surfaces. Consequently, the use of glass lens components in disposable endoscopes is preferably minimized to reduce cost. Polymeric lenses, on the other hand, may be manufactured by cost-effective injection molding techniques. Accordingly, the incorporation of polymeric lenses in a disposable endoscope is preferably optimized to minimize cost while still providing acceptable optical effectiveness.
Several conventional endoscopic relays lens systems also incorporate rods or cylinders to enhance transfer of the light through the optical train. For example, U.S. Pat. No. 4,946,267 to Hoogland teaches an endoscopic relay optic design including an assembly having a central rod-like transfer element with first and second negative and positive optical elements attached to each end of the rod like element. The optical elements are directly cemented to each other and to the rod-like element to form a single unit which is subsequently positioned within the lens tube of the endoscope during assembly.
The disadvantages regarding the manufacture of conventional systems are apparent. First, glass positive and negative elements must be individually formed by expensive optical grinding and polishing techniques, thus, adding further cost to an already expensive instrument. Second, assembly of the system requires cementing of the glass and/or polymeric optical elements to each other and then optionally to rod-like elements, thereby requiring additional steps during manufacture. In addition, where a rod-like element having flat end surfaces is used the end surfaces must be ground and polished to a precise finish so as to minimize undesired light scattering or absorption by these surfaces.
In accordance with conventional replica molding processes, a master mold having a surface which is the negative replica of a desired lens surface to be provided is positioned adjacent a substrate. Thereafter, a few drops of low-shrinkage epoxy are pressed out into a thin layer between the master and the substrate. The epoxy is cured and the master is removed leaving a precise negative replica on the substrate. Replica molding processes are commonly used to form opthamalic lenses, mirrors, correction plates, fresnel lenses, video discs and diffraction gratings. See for example, U.S. Pat. Nos. 4,957,663, 4,615,847, 4,484,798, 4,367,014 and 3,917,766.